In recent years, a transmission system that includes multiple rings has been designed to improve the efficiency of data transmission. Further, in order to construct a large-size network, implementation of a multi-ring configuration in a transmission system has been considered in which multiple rings are connected to each other. Hereinafter, a transmission system in which multiple rings are connected to each other will be also referred to as “a multi-ring transmission system”, and a communication network including multiple rings will be also referred to as “a multi-ring communication network”.
Implementation of a bi-directional line switched ring (BLSR) scheme has been proposed as a method for ensuring a redundancy of a multi-ring transmission system based on a synchronous digital hierarchy (SDH). In the BLSR scheme, for example, a data transmission node positioned along a ring in which a plurality of nodes are connected to each other in a ring topology sets a pair of redundant path segments including a working path and a protection path along the ring, and the data transmission node transmits data in one direction along the ring in a normal operational state through the working path along the ring. In the BLSR scheme, when a failure has occurred at the working path, an active redundant path segment for actually transmitting data is switched from the currently-used redundant path segment (the working path) to an alternative redundant path segment (the protection path), and the data is transmitted in the opposite direction along the ring through the alternative redundant path segment (the protection path).
Japanse Laid-open Patent Publications Nos. 2002-232442, 10-224389 and 2007-194957 are examples of the related art.